Which of the following fill the lungs and appear as tiny end ducts of branching airways?

Question

Quizplus · Accepted Answer

Alveolar ducts fill the lungs and appear as tiny end ducts of branching airways.
Cilia lines the upper respiratory tubules, and they are responsible for trapping debris and keeping foreign objects from entering the lungs. 
Hemoglobin is responsible for the transportation of oxygen from the lungs to the body tissues and it then returns the tissue's carbon dioxide to the lungs. 
Ions are atoms with a positive or negative electrical charge.

Which of the Following Fill the Lungs and Appear as Tiny